The pH is a measure of the acidity of the body. One definition of an acid is a chemical that donates a proton, which is the same as a positively charged hydrogen ion. As the opposite of an acid, a base is a chemical that accepts a hydrogen ion. In the body, a neutral or normal pH in the blood is 7.4. A lower number, such as 7.2 is acidic, while a higher number such as 7.6 is basic or alkalotic. It is important to consult with a physician regarding health related issues and for diagnosis and management of health disorders.
The pH scale
The pH scale is a mathematical way of expressing the concentration of hydrogen ions in a solution such as the blood. The pH in a solution usually varies from 0, which is highly acidic to above 14, which is highly basic, but can go below zero or above 14. In the blood, if the pH varies by less than one unit, to 6.4 or 8.4, that is usually more than enough to cause death. Small changes in pH represent very large changes in the acidity.
Physiology
The pH is largely controlled by buffers in the blood, the rate and depth of breathing, and the actions of the kidneys. A buffer is a weak acid and base mixture. When acid is added to the blood, weak bases bind it, keeping the blood at a neutral pH. Likewise, when base is added to the blood, weak acids release protons to keep the blood neutral. The primary buffers include carbonic acid and proteins, which are found throughout the blood. When the buffer systems become overwhelmed, the lungs and kidneys are generally able to compensate.
Regulation
The process of metabolism produces the gaseous byproduct carbon dioxide, which is then combined with water in the blood to make carbonic acid that is then transported to the lungs where it is converted back into water and carbon dioxide. The carbon dioxide is released out of the lungs. Decreasing the rate or volume of breathing per minute increases the acid in the blood, and vice versa. However, some acids, such as sulfuric and phosphoric acids produced from protein metabolism cannot be disposed of through the lungs, and, instead, the kidneys dispose of these acids in the urine and also regulate the concentration of the base bicarbonate in the blood.
Consequences
Normal pH of the blood is important for proper cellular function. Excess acid or base effects the actions of structures inside and outside cells such as enzymes, protein channels, electrical conduction, metabolism and cells of the immune system.
Causes of Imbalance
Acid-base imbalances are divided into respiratory causes and metabolic causes. Respiratory problems, such as asthma, interfere with the normal exchange of carbon dioxide and lead to carbonic acid buildup or loss with a change in pH. Metabolic problems, such as toxin ingestion or kidney failure, can make excessive acids or bases, or prevent their secretion.
References
- "Physiology"; Linda S.Costanzo; 4th Ed 2008
- "Harrison's Principles of Internal Medicine"; Anthony S Fauci, et al.; 17th Ed 2008
